<!DOCTYPE html>
<html>
  <head>
    <meta charset="utf-8">
    <meta name="viewport" content="width=device-width,initial-scale=1.0">
    <title>demo1</title>

    <link href="https://cdn.jsdelivr.net/npm/animate.css@3.5.1" rel="stylesheet" type="text/css">
  </head>
  <body>
    <div id="app"></div>
    <!-- built files will be auto injected -->
  <script>
    (function (doc, win) {
      var docE1 = doc.documentElement,
        resizeEvt = 'orientationchange' in window ? 'orientationchange':'resize',
        recalc = function () {
          var clientWidth = docE1.clientWidth;
          if(!clientWidth)return;
          if(clientWidth>750){
            docE1.style.fontSize = "18px";
          }else{
            docE1.style.fontSize = 50*(clientWidth/750)+"px";
          }
        }
        if(!doc.addEventListener) return;
        win.addEventListener(resizeEvt, recalc, false);
        doc.addEventListener('DOMContentLoaded', recalc, false);
    })(document, window)
  </script>
  </body>
</html>
